It has previously been proposed to prepare highly swelling polymers from unsaturated carboxylic compounds such as maleic anhydride by polymerizing the carboxylic monomer with a cross-linking agent such as a polyethylenically unsaturated compound as shown in U.S. Pat. No. 2,798,053. Such polymers have been employed as synthetic gums to produce mucilaginous or gel-like aqueous compositions.
It has further been suggested to employ solid linear copolymers of maleic anhydride and styrene in admixture with a substantial proportion of a polyhydric alcohol, as for example in U.S. Pat. No. 3,085,986, to produce thermoset molded resins wherein the final product is cross-linked by reaction of the polyhydric alcohol with the anhydride residues in the linear polymer. The products from this latter procedure are hard resins which absorb only minimal amounts of water or sodium chloride solution even after immersion therein for seven days.
It is known from U.S. Pat. No. 3,810,468 and Ser. No. 331,849, filed Feb. 12, 1973, that lightly crosslinked absorbent fibers can be prepared from copolymers of maleic anhydride and vinyl monomers wherein the crosslinking agent is a glycol or an alkylene diamine. However, these fibers are stiff and brittle.